horse-power
Definition
- Noun (uncountable):
- Unit of power: "horse-power" is a unit for measuring the power of engines, motors, or other machines. It is defined as the amount of work required to lift 550 pounds one foot in one second (equivalent to approximately 746 watts in the metric system). The term is often abbreviated as "hp" or "HP."
Usage Examples
- (The engine's power output is 200 hp.)
- (The machine's power is measured in hp.)
- (Historical context of the unit.)
Advanced Usage
"Brake horse-power": the measure of an engine's power before losses in the transmission system (e.g., from the crankshaft).
- The engine's brake horse-power is 150 hp, but the wheel horse-power is lower due to friction. (Power measured at the engine output.)
"Metric horse-power": a slightly different unit used in some countries (1 metric hp ≈ 735.5 watts).
- In Europe, car engines are often rated in metric horse-power rather than imperial. (Alternative standard.)
Variants and Related Words
Horsepower (n, often written as one word): the same unit; common in modern usage without a hyphen.
- The motor's horsepower rating is 100. (Power measurement.)
Horsepower-hour (n): a unit of energy equal to one horsepower used for one hour.
- The generator produced 500 horsepower-hours of electricity. (Energy measurement.)
Synonyms
- Power rating: the numerical value of power output.
- Mechanical power: the rate of doing work, often expressed in watts or hp.
Related Idioms
- "Putting the horse before the cart": not directly related to horse-power, but a common idiom about order of operations.
- "A horse of a different color": unrelated to power; means a completely different matter.
Notes on Usage
- The term "horse-power" is primarily used in engineering, automotive, and industrial contexts. It is rarely used for human or animal power today.
- The hyphen is optional in modern writing; "horsepower" is more common in technical texts, while "horse-power" appears in older or formal contexts.